ABSTRACT
Lactic acid bacteria (LAB) constitute a group of gram-positive bacteria united by a con-
stellation of morphological, metabolic, and physiological characteristics. The general
description of the bacteria included in the group is gram-positive, nonsporing, nonrespir-
ing cocci or rods, which produce lactic acid as the major end product during the fermenta-
tion of carbohydrates. The LAB term is intimately associated with bacteria involved in
food and feed fermentation, including related bacteria normally associated with the
(healthy) mucosal surfaces of humans and animals. The boundaries of the group have
been subject to some controversy, but historically the genera Lactobacillus, Leuco-
nostoc, Pediococcus, and Streptococcus form the core of the group. Taxonomic revi-
sions of these genera and the description of new genera mean that LAB could, in their
broad physiological definition, comprise around 20 genera. However, from a practical,
food-technology point of view, the following genera are considered the principal LAB:
Aerococcus, Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc,
Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus, and Weissella.
The genus Bifidobacterium, often considered in the same context as the genuine lactic
acid bacteria and sharing some of their typical features, is phylogenetically unrelated
and has a unique mode of sugar fermentation. The classification of lactic acid bacteria
into different genera is largely based on morphology, mode of glucose fermentation,
growth at different temperatures, configuration of the lactic acid produced, ability to
grow at high salt concentrations, and acid or alkaline tolerance. Chemotaxonomic markers
such as fatty acid composition and constituents of the cell wall are also used in classifi-
cation. In addition, the present taxonomy relies partly on true phylogenetic relationships,
